1. Field of the Invention
This invention relates to calender roll machines, and more particularly to apparatus to effect bending forces within a roll in said machine.
2. Prior Art
Bending of rolls in calender roll machines has been done for many years in order to create a constant line of pressure over the entire width of a roll gap in a wide line pressure range. These conditions are required by paper mills, textile mills, web plastic manufacturers and other industries, because non-uniform line pressures in the nip or pressing gap can easily reduce the quality of the product flowing therefrom, and can impair the productivity of the machines. It is difficult to maintain these uniform gap conditions because of varying loads on the roll and supporting bearings. If resultant forces on these components are to be controlled, they can cause the cost and complexity of the components to escalate considerably. A number of attempts have been tried to control roll bending. One is shown in U.S. Pat. No. 4,068,360 to Frueler wherein fluid pressure is supplied to support devices within the roll, and piston and cylinder units press in a direction normal to the roll to effect bending therein. U.S. Pat. No. 4,030,177 to Hold discloses deflection correction by piston and cylinder units effecting a moment arm around the roll bearings, utilizing sensors which trigger the external bending of an inner shaft to counter any deflection of the external roll. The piston and cylinder units are located either between the bearings or distally arranged therewith. U.S. Pat. No. 3,543,365 to Helminen shows a web stretching device wherein a portion of the roll axis is pivoted about its support bearings.
Though these prior devices have counter deflected shafts or rolls, they appreciably increase the loading on the equipment and thus they pay a price in necessarily heavy bearings, excessive bearing wear and the need for frequent replacement thereof.
Thus it is an object of the present invention to provide roll bending apparatus which will minimize additional loading on the roll bearings.
It is a further object of the present invention to provide a roll bending apparatus that will permit a change in the nip condition of a roll by the application of a couple to each end of the roll.